The invention concerns a process and a device for separating broken materials consisting of broken corns or beans and their shells, especially for the separation of broken cacao beans, so-called nibs, from the cacao bean shells.
As used herein, the term xe2x80x9cbroken goodsxe2x80x9d and xe2x80x9cbroken materialsxe2x80x9d shall mean fractionated agricultural products of the type having an inner bean (or other meat) covered by shells (or skins or husks) which must be separated. Although applicable to a range of such products including, for instance, corn, the invention will be described with particular reference to cacao beans. Fractionated cacao beans with a maximum of about 2% shells are referred to as xe2x80x9cnibsxe2x80x9d, and fractionated shells are referred to as xe2x80x9cshellsxe2x80x9d.
Cacao beans exiting, depending on the kind of their preparation, from a roasting plant, sterilization plant or pre-drying plant are usually broken or fractionated in a reflex breaker. The fractions of broken cacao beans, the so-called nibs, arising from that kind of preparation, as well as shells have then to be separated from one another so that the nibs can be further treated. The accuracy of separation must be as great as possible, as it influences essentially the quality of the manufactured cacao mass. At maximum 2% shells are allowed within the nibs in accordance with certain regulations. Moreover, the portion of shells within the nibs should be as small as possible resulting in an essential improvement of the operation time of the following grinding station.
Up to now the nibs are separated from the shells by screening into different fractions and by subsequent sifting the several fractions. In a special plant of the assignee the cacao beans are for that reason automatically delivered from preceding machines to a large preceding screen and are thereafter fed to the breaking station and grading station. The cacao beans broken in a rotating double disk breaker are separated in a classifying apparatus into six fractions. The mixture of shells and nibs exit laterally from the screen box in trajectories of parabolic flows separated into fractions to a separate vertical sifter. An adjusted air stream which is coordinated with the nib size of each fraction achieves a good separation of the specifically heavy nibs from the specifically lightweight shells on the principle of counterflow sifting. The grading station is provided with five cascade-shaped screens arranged one behind the other, which separates the broken cacao beans into six fractions from coarse to fine. The applied coarse to fine sift principle resulting by means of short paths of the main quantity in short contact times and provides advantages in microbiological and hygienic aspects. The sifting of the individual fractions takes place in six laterally arranged vertical sifters. By reason of the fine distribution of the sifting into six fractions, a higher separating effect at a more precise screening is achieved at a high through-put rate. The air velocity of each sifter can be adjusted to the optimum separating effect. The shell fractions are thereafter drawn upwardly, separated from the air in six shell separators and extracted via a common shell trap. The nibs fall downwardly into a vibratory discharge channel. The above mentioned plant, however, has certain disadvantages in constructional and operational aspects, although the results concerning the classification of the broken beans into fractions as well as the separation of the shells from the nibs are rather good.
Therefore, it is an object underlying the invention to further improve the above mentioned process and apparatus for separating broken materials, especially broken beans of cacao, i e., so-called nibs, from the shells of those beans, and to minimize in this respect the cost of the apparatus and machines necessary, resulting, however, in a separation rate which is at least so high as for the prior art process and apparatus.
These and other objects are advantageously solved by a first combination of steps of the process according to which the separation of the broken goods is accomplished electrostatically by electrically charging the broken goods in a fractionated configuration within a charging area between two differently charged electrodes and thereafter by directing the electrostatically charged fractionated broken goods in a free downfall in another homogenous electrical field provided by two other electrodes defining the way of downfall of the broken goods, resulting in the broken goods being at least partly differently deflected and thereby also separated, so that the nibs are separated from the shells, and are thereafter by means of a mechanically operating separator collected and delivered in two different product streams, consisting essentially of a stream of nibs and a stream of shells.
The basic of the invention is that the separation is accomplished electrostatically in one or several steps by charging the particles of the broken goods in a homogeneous electrical field and thereafter deflecting the charged particles in another electrical field by forces which are proportional to the specific charge. This idea is based on the known fact that the size of the particles influence the separation insofar as with increasing particle size the ratio of surface to volume becomes more and more unfavorable and thus the specific charge will be smaller. The electric conductivity, too, of the particles, has influence in this connection as it is the physical parameter defining the rate at which the particles are changed. Moreover, it must be considered that the shells and nibs have in general the same specific gravity, so that a different deflection of particles having the same size can only be expected if during the charging the particles are provided with different charges.
Considering the above mentioned physical facts and according to an especially advantageous embodiment of the process of the subject invention, the fractionated broken goods are subjeted to vibratory movement during the charge transfer from the charged electrodes to the broken good as they pass through the charging area to the area of free downfall, and the vibratory movement can be controlled in order to adjust the length of stay of the broken goods within the charging area and thus the duration of charging. The broken goods are deflected within the area of free downfall, in accordance with the amount of charge they received in the charging area and thus the quantity of charge the broken goods have for deflecting the broken goods toward the cathode one of the electrodes which is connected to ground. During said deflection, part of the more light-weight (lighter) and smaller particles of the broken goods are so strongly deflected in the area of free downfall that this part passes through apertures provided in the cathode and is fed behind these apertures through a channel to a product stream of shells.
Moreover, it is advantageous to control the moisture content of the stream of broken goods before the charging area to the requirements of the electrical charging of the particles of the broken goods, as the conductivity of the material can change dependent on the content of moisture and particles with different moisture content will therefore be differently deflected.
Furthermore, to optimize charging and separation of the broken goods thereafter into, larger, heavier and smaller, lighter portions, a vibratory or shaking means is used within the charging area adjacent to the electrodes. This results in most of the particles of the broken goods being spread to be positioned in a one-nib-layer only, as in the case that several particles are positioned one over the other in several layers the charging can be hindered because no direct contact between the upper most positioned particle and the charged surface of the apparatus will then be provided.
The apparatus for providing the process according to the subject invention is characterized generally by a charging area for the electrical charging of the broken goods which is to be separated, moreover by a deflection area adjacent thereto for the deflecting the charged broken goods during a free downfall, and by a separating area connected thereto for the separation of the at less deflected heavier particles of the broken goods from the more deflected light particles as well for the removal of the separated broken good.
In this connection it has been found advantageous to configure the charging area such that it is provided with at least a feeding hopper for the broken goods which is to be separated and with at least a vibratory chute adjacent thereto and being in feeding connection with said hopper, which chute is provided with differently charged electrodes between which the broken goods which are to be separated are moved through in order to become electrically charged. The deflecting area is provided with at least two further electrodes defining the free downfall section, and a separation area joining the deflection area is provided with at least one adjustable mechanical separator which is connected to a transporting system for the separated product streams, consisting of nibs or heavier particles of the broken goods and shells of cacao beans or lighter particles of broken goods.
One of the two electrodes defining the deflection area is advantageously a cathode connected to ground and is provided with several apertures having flaps for the further deflection of the deflected shells of the cacao beans, behind with apertures a channel is provided connected to a transport system for the removal of the shells of the cacao beans, i.e. the smaller, lighter particles of the broken goods.
Moreover, it is advantageous to configure one of the two electrodes connected to the vibratory chute to become a cathode connected to ground, which cathode supports the transfer of the charge to the particles of the broken goods, whereas the vibratory chute is completely electrically insulated to the outside and is connected to same voltage as one of the electrodes. Those electrodes related to the vibratory chute may advantageously consist of plastic material covered by metal or may advantageously be embedded into the chute such that the one electrode is located in the bottom of the chute and the other one is distantly positioned above the bottom so that the charged broken goods can be fed through between the electrodes. The anode of the two electrodes is connected to a positive or negative DC voltage.
According to another aspect of the invention the vibratory chute may be provided with an adjustable vibratory drive and the level of the feeding hopper may also be adjusted in order to make the feeding height considerably variable.
Moreover, according to a further aspect of the invention the inner wall of the vibratory chute may be provided with contours supporting the particles of the broken goods during their movement over these contours, which may be configured in form of pro-tuberances.
According to a further aspect of the invention the two electrodes of the apparatus defining the downfall section of the deflecting area may be configured as condenser plates and may be provided with an electrically insulating layer of material in order to avoid a possible change of charge if the electrodes contact particles of the broken goods.
As discussed above in describing the process of the invention, the apparatus can be provided with means for controlling moisture content of the broken goods in order to provide a uniform degree of moisture in the broken goods, as the efficiency of transfer of the charge is dependent inter alia on the moisture content.
Concluding the above mentioned advantageous embodiments of the invention, it must be stressed that in case the entire apparatus should operate under special climate conditions, it has been found advantageous to enclose the apparatus in a housing. Multiple separating means can be located serially one behind the other or operated in parallel in the housing or enclosure.
The above mentioned objects of the subject invention are also advantageously carried out by a second combination of steps of the process, according to which the broken goods are separated electrostatically by charging them in fractionated configuration within a charging area between two differently charged electrodes and is simultaneously subjected to a vibrational movement, the intensity of which is controlled in order to adjust the charging time of the broken goods, especially broken cacao beans and cacao bean shells.
According to further advantages of the process the fractionated, electrically charged broken goods are separated through the vibrational movement by means of a suction airflow applied to the broken goods, thus that the shells are suctioned off the broken goods. The shells are then separated from the air within a cyclone-separator, whereas the nibs are delivered in a separated product stream.
In order to further optimize the separation of the broken goods, the broken goods are electrically charged within the charging area by the electrodes within a vibration apparatus such that the shells are lifted over the bottom of said vibration apparatus and are then suctioned off by means of a suction apparatus, whereas the broken nipbs remain essentially on the bottom of said vibration apparatus where they are moved to the outlet end of said vibration apparatus because of the vibratory movement.
The apparatus for providing the process of the subject invention according to the above mentioned second combination of steps is characterized by a charging area for the electrical charging of the broken goods to be separated, comprising at least one hopper receiving the broken goods to be separated and at least one vibratory chute joining the hopper for feeding the broken goods, which chute is provided with the differently charged electrodes, a positively charged anode and a cathode connected to ground generating a homogeneous electrical field, between which the broken goods which are to be separated atre passed in order to become electrically charged, moreover comprising a deflection area provided with a suction apparatus for the lighter shells of the broken goods, and further comprising a separating area for the separation of the shells from the stream of suctioned-off air provided with at least one apparatus for winnowing shells from the air.
In this connection it is essentially advantageous to provide the suction apparatus with at least one hood positioned over a perforated plate being the cathode connected to ground within the area of the roof of the vibratory chute, which hood is joined through a suction tube to the winnowing apparatus in form of a cyclone, connected through a discharge air tube to a suction fan and provided at its lower end with a receiving container for the separated shells.
Other and more specific objects and features of the invention herein will appear from the following detailed description and claims, taken together with the drawings.